SURFACE MOUNT CHALLENGES WITH LEAD-FREE REFLOW

Abstract: Lead-Free (LF) processing has been gaining importance with the growing economic momentum and impending legislation. This paper focuses on the reflow process and the challenges posed by the LF conversion on surface mount assembly. The differences in melting point between eutectic and LF solders, along with the constraints imposed by the sensitivity of the components imply that the reflow process has to be carefully defined. It is also of vital importance to ensure that a processing range is chosen so that it can be easily monitored and controlled. The LF reflow process is described in greater detail, along with the low and high temperature constraints on processing window.

The lowest peak temperature and time above liquidus (TAL) are experimentally determined using designed experiments. Limits are identified for these variables, which in turn define the processing window. The resulting profile is then compared against a traditional eutectic profile, to determine the impact of beat rate and delta temperature, followed by a discussion on power cost adder due to the higher reflow temperature associated with LF processing.

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